GB2535320A

GB2535320A - Portable traffic light control system and portable traffic light signal

Info

Publication number: GB2535320A
Application number: GB1601700.6A
Authority: GB
Inventors: Michael Hutchinson Peter
Original assignee: AGD Systems Ltd
Current assignee: AGD Systems Ltd
Priority date: 2015-01-29
Filing date: 2016-01-29
Publication date: 2016-08-17
Anticipated expiration: 2036-01-29
Also published as: GB201601700D0; GB201501513D0; GB2535320B

Abstract

A control system, having at least one traffic light, for controlling the flow of traffic across a controlled highway. The traffic light has a signal head 10a including a set of lights, a portable FMCW radar detector 30 which monitors a zone in front of the traffic light at a defined range through which the flow of approaching traffic passes. The radar detector generates an output signal that includes information about vehicles identified in the zone of detection, the information including speed and position. A controller receives the output signal from the radar detector and derives a demand signal; the demand may be based on the number of vehicles approaching or stationary at the lights or a model based on historical variations in demand. The controller determines the relative duration of the green to red signal as a function of the demand signal. The system may be battery powered and the FMCW radar may have a duty cycle of less than 20%.

Description

PORTABLE TRAFFIC LIGHT CONTROL SYSTEM AND PORTABLE TRAFFIC LIGHT SIGNAL

This invention relates to improvements in portable traffic light control systems, and to a portable traffic light signal. it in particular relates to portable traffic signals.

It is commonplace to control the flow of traffic across a junction using traffic light signals. In a most simple form the traffic light system may comprise two traffic light signals, otherwise commonly referred to simply as traffic lights, each controlling the flow of traffic through the junction in a respective direction. At any time, a first traffic light may be set to stop the flow of traffic towards that light, and the second traffic light may be set to allow traffic flow across the junction towards the first traffic light. The traffic lights will then swap over, so that the traffic is allowed to cross the junction from both directions in turn. In a more complex system, there may be three or four or more traffic lights, each synchronised to the others to control the traffic flow.

The relative green phase time to red phase time of each traffic light is typically preset, according to the expected traffic volumes. This is set according to a defined sequence. For instance, if one of the approaches is a major road and the other a minor road, the amount of relative green time for the traffic light controlling the major road may be relatively higher than the amount of green time for the traffic light controlling the minor road. The sequence may vary for different times of day to account for "tidal flow" of traffic, such as that due to commuting traffic. In a more complex system the light sequence may be controlled centrally from a control room, known as urban traffic control (UTC). In this case, the timing of the lights may also be varied independently of UTC control to account for the traffic demand based on permanent sensors mounted in the road, usually inductive loop based sensors.

in addition to permanent traffic light installations it is commonplace to deploy portable traffic light signals for temporary installations. These may be used in place of permanent traffic lights if there is a fault, and are also used at temporary road works where there is a need to control the flow of traffic. Typically, a two lane road may be reduced to one lane at road works, and to allow vehicle to move along the one lane in both directions lights are used to ensure vehicles can take turns using the one lane for flow in both directions.

A portable traffic signal typically comprises a signal head supported above a base by a pole. The base is usually provided with wheels to allow it to be easily moved around manually by one person although some have rollers. The signal includes a driver that produces drive signals for the lights from a set of timing signals. These signals may be stored in a memory of the traffic signal in the case of a "master signal" or will be received by a "slave signal" from a master traffic signal, typically communicating using radio frequency transmissions. The lights are almost always battery powered and will include one or more batteries. The portable nature of the traffic light allows it to be easily moved around for use at a temporary installation, and in order to allow maximum flexibility the portable traffic signal should be largely self-contained and able to operate in areas without external power supplies or at least without the need to make a connection to the permanent supply unless that is preferred.

Radar detectors have been used to activate green phases on portable traffic lights for over 40 years. They function by transmitting a radio frequency beam and detecting reflected portions of that beam from objects in the field of view of the radar detector.

The radar detector may be supported by the same support mast as the signal head, and is oriented so that it monitors a wide area in front of the traffic light where a vehicle would enter when approaching the traffic light from the front. If there is a vehicle anywhere in this area and the traffic light is red, but no detected vehicle at the light that is currently green, the red light may be forced to green ahead of any stored pre-planned sequence. This minimises the wait time for vehicles, especially at quiet times of the day when there is little traffic.

The radar detector apparatus of the prior art provides information for the system indicative of whether a vehicle is present in front of a traffic light giving a simple (on/off) demand signal. This means the following; * When there is no traffic at one end no demand is created * When traffic arrives at one end, a demand is created but this demand is only yes for green * The same yes demand is generated whether it is one car approaching or 20 cars.

* if you have one car approaching/queuing one end and 10 cars approaching/queuing at the other the demand is equally requested for green.

These current systems can lead to significant dynamic imbalance of the system.

According to a first aspect the invention provides a portable traffic light system suitable for controlling the flow of traffic across a controlled region of highway, such as a junction, the portable traffic light system comprising: at least one portable traffic light that in a position of use controls a flow of traffic that is approaching the controlled region, the traffic light comprising a signal head including a set of lights that in use is located so that the lights are visible to vehicles approaching the controller region; a portable radar detector apparatus having a range detection capability which in a position of use monitors a detection zone that extends over a region in front of the traffic light at a defined range through which the flow of traffic approaching the traffic light must pass, the radar detector generating an output signal that encodes information about any target vehicles identified in the zone of detection, and a controller that in use receives the output signal from the radar detector apparatus, the controller being arranged to derive from the signal output from the radar detector apparatus a demand signal and in which the controller is further adapted to determine the relative duration of the green to red signal for the light as a function of the demand signal.

The invention therefore provides a portable traffic light system which is able to take account of the demand on the signal through the use of radar based range information. This provides enhanced control or a traffic light controlled junction compared with the prior art systems which do not include any range functionality.

The detection zone may correspond to a narrow range of distances, for instance a zone with a width (measured in a direction away from the radar along the path of flow on the oncoming vehicles) of less than 2m, or even a single specific distance whereby the width of the zone is determined solely by any margin of error in the detection ability of the radar, for instance 200m away plus or minus I metre. In this case, the system may be arranged to identify vehicles entering or exiting the zone, or both entering and exiting the zone, so as to output a vehicle count signal. For example, as each new vehicle is identified in the zone a count signal may be incremented by one count.

The detection zone may be much larger, for lstance able to contain more than one vehicle. The zone may extend from the radar detector apparatus away from the apparatus, or may extend from a point some distance from the detector apparatus away from that point. For instance, the start of the zone may be aligned with a stop sign or stop line associated with the traffic signal.

A zone covering a range of distances of, say 50m-for instance extending over a region bounded at one end 100m and that other end 150m away from the radar, or spanning an area extending from a stop line for a distance of 50m away from the stop line-would be able to contain a line of perhaps 10 or more vehicles at any time. In this case, in addition to a count (or as an alternative) of vehicles approaching or waiting at the traffic light, a signal indicative of the number of vehicles in the zone may be determined. For instance if there are three vehicles identified in the zone at any given time the output signal may have a value of three.

In each case the speed of the vehicles entering, exiting, or within the detection zone, may be output. This may be achieved by the range detection facility of the radar by measuring the change in position of identified target vehicles over time. it may be achieved using the Doppler effect. The position of each vehicle may also be output from the radar. Both the position and speed may be used in the determination of the demand signal.

By demand we may therefore mean the volume of traffic approaching the signal through the detection zone as indicated by a count, or the volume of stationary traffic, or a combination of the volume of moving and stationary, or a combination of a binary measure of stationary and moving traffic c.g. is there some stationary traffic and is there some moving traffic. The significant feature is that the demand is no longer a binary signal as in the prior art but a much richer signal indicating the level of demand on a non-binary scale.

The system may be adapted to weight the relative green on and red off time for each of the traffic lights according to the demands. This provides a significant improvement over a simple prior art arrangement that only determines if there is traffic or not traffic present.

The portable controller may be built into the traffic light, or built nto the radar detector or a stand-alone portable unit.

The radar detector apparatus may be physically connected to the traffic light. For instance, the signal head may be supported above a base by a mast, and the radar detector may also be supported by that mast.

Locating the radar detector apparatus near to the traffic light signal head means it will have a good view of approaching traffic and can "see" more than just the leading vehicle provided it is high enough up or slightly to the side of the highway. For instance, it may be located at least 2m above the ground level, and may be located between Om and 2m to the side of the highway so that it looks across the highway at an acute angle.

Alternatively, the radar detector apparatus can be fixed temporarily to the local infrastructure, such as a disabled permanent traffic light, or perhaps supported by a dedicated portable support mast.

Where the radar detector is not an integral part of the traffic light, the output signal may be sent to the controller by a radio connection to send (and possibly receive) information.

Because the radar detector apparatus has a range detection capability, which can be achieved by selecting a radar detector of the modulated frequency type, it is capable of measuring the distance (range) to each target identified in the zone of detection but can also determine the position of each vehicle at a given instant in time. This may be expressed as a combination of distance to the target and the angle of the target relative to a known datum.

The radar detector may output the range, speed or the position of a vehicle in the detection zone or any combination of the tree in the detection zone. It may do this for all vehicles in the detection zone at any given time.

The radar detector may output a count indicating the number of targets identified as individual vehicles in the detection zone.

The radar detector may output a count indicating the number of vehicles entering or exiting the detection zone. The system may reset the value of this count when an associated traffic signal turns red to provide an estimate of the number of vehicles between the detection zone and the traffic signal.

When updating the count, the system may reset to a new value which is dependent on the number of vehicles known to have passed across the junction controlled by the traffic signal. This information may be determined by monitoring the number of vehicles moving away from the junction.

Therefore the zone of detection may be set to encompass vehicles moving away from the traffic signal as well as moving towards it. Combining the information from a radar detector on each entrance/exit to the junction enables an accurate reset of the count signal to be made since the sum of vehicle entering and exiting the junction should come to zero.

The zone of detection of the radar detector apparatus may extend for at least 10m and preferably at least 50m or at least 100m in front of the traffic signal. This allows another of identified targets to be determined when there is a queue of traffic. For instance, the size of the zone may accommodate at least 10, or at least 20 or more stationary vehicles queuing at the traffic signal.

The system may be arranged to divide the portion of highway in the detection zone ahead of the traffic signal into a plurality of segments and the radar detector apparatus and controller may be adapted to measure the number of cars approaching the traffic signal that arc within the detection zone and the number of segments of the detection zone that contain a stationary vehicle. In addition it may ouput range and angle information, e.g distance and position. The estimate of volume of traffic may be generated by processing this information and this may be used in producing the demand signal.

The radar detector apparatus may therefore output an output signal that encodes one or more of the following items of information about vehicles in the zone: The number of vehicles (although the controller may determine this from the output signal); - The location of each vehicle in the zone The Speed of each vehicle - Is a vehicle stationary (yes/no binary signal) The number of vehicles in each section of the zone.

The type of vehicle as indicated by the strength of reflected signal from one or more targets seen by the radar apparatus.

This output signal may be used to produce the demand signal.

Each section may correspond to a portion of highway of between lm and 10m in length, or between lin and 5m in length, or between 2m and 5m in length, or any length between lm and 20m or so. The size of each section is preferably chosen so that only one stationary vehicle may be located in each zone, i.e. the length of the zone equals the length of an average vehicle plus an amount to allow for the spacing between vehicles, approx. I m The controller may be adapted to estimate the demand as a function of the volume of traffic. It may do this by adding the number of segments that are occupied by stationary vehicles to the number of vehicles approaching the rear of the queue of waiting vehicles to create a demand value.

The controller may produce a demand value in other ways. For example, the controller may process the output signal (for instance a count signal that is dependent on the number of cars approaching the traffic signal and the velocity of the approaching vehicles), and may weight the demand value according to those parameters. It may additionally weight the demand value as a function of the type of vehicle detected, giving more weight to certain types of traffic compared with others.

The demand value may be produced at times when the traffic signal is on red, or at all times e.g. when red and also when green.

The controller may produce timing signals that are supplied to the traffic lights whereby the higher the demand signal the higher the relative duration of green to red phase, and the lower the demand signal the lower the relative duration of the green to red phase. Thus, when there is more demand the light will spend more time on green to help the traffic pass.

in a preferred arrangement the system comprises two or more portable traffic light signals each comprising: a traffic light signal head including a set of lights that in use is located so that the lights arc visible to vehicles approaching the respective traffic light; and may include for at least two of the traffic lights a respective radar detector apparatus with range detection capability that monitors a detection zone which extends over a length of the highway approaching the respective traffic light through which traffic must pass or will be stationary approaching the traffic light.

A controller may be associated with each of the radar detector apparatus of each traffic signal, or one controller may receive the output from both radar detector apparatus to produce a demand signal for each traffic light. The controller may generate a demand signal for each traffic light.

The system may include a processing means arranged to process together the two demand signals to produce a weighted demand for each traffic signal that takes account of the demand at each traffic signal. Therefore, rather than simply basing the demand for a traffic signal on the signal output from respective radar detector the weighted demand takes account of the relative demands across multiple traffic signals.

This processing means may comprise a part of the controller where a single controller is provided, or may be part of one controller and receive demand signals from the other controllers for use in producing the weighted demand for each traffic light.

The weighted demand for each traffic signal may determine a forced green time to be sent to each traffic light which determines when the light should turn green. The general concept of providing a forced green signal to a traffic light is well known and the way in which it is used by the light to modify a pre-programmed timing sequence will therefore not be explained in any greater detail in this application. The forced green time may be considered to be a request that the light turns to green as soon as it is safe to do so or as soon as it is possible to do so whilst respecting any other constraints placed on the operation of the system.

The forced green time may be deployed for each signal to account for the identified traffic flow. The weighted demand signal may therefore comprise timing information for the traffic light signal.

Each traffic light signal may include a receiver that receives the weighted demand value for that signal, or other related timing signals produced by the controller, and a driver that produces drive signals for the lights of the signal head in response to the weighted demand signal.

The processing means may produce a forced green time for each light that maximises the overall flow of traffic through the controlled portion of highway.

in an alternative to forced green times, the weighted demand may be representative of the percentage of time each light should be on green rather than red (or on red rather than green). It may be expressed as a fraction or ratio, or as absolute times in seconds. This information may be post processed to produce timing information for each traffic light.

Therefore, the weighted demand signals from the processing means may give a higher priority to traffic approaching one traffic signal compared to the other, so for the same traffic demand at each traffic signal one may have a higher relative green time than the other.

The processing means may take account of other factors, such as the time of day. For instance, with a tidal flow priority may be given to one traffic signal early in the day in the direction of traffic travelling into a city and at a later time of day may give priority to the other traffic signal.

The processing means may generate weighted demand signals using an evolving model of flow of vehicles across the junction that is updated by the information contained in the output signals from radar apparatus or from the demand signals for each traffic signal/radar apparatus.

For example, in one arrangement the processing means may generate weighted demand signals in which the green time for a traffic signal does not have to represent the value of the demand signal at an instant of time corresponding to a current traffic light cycle (one cycle for instance being a period of time between a light turning from red through green and back to red again, or green through red and back to green again, or just the time spent on red or on green) but may be a function of historical variations in the demand signal value over time.

The generation of weighted signals based on historical demand signal values may enable the system better to take account of the way traffic moves.

The evolving model may be arranged so that there are only gradual changes in the cycle times for each light regardless of the change in demand values. The model may therefore include a time dependent filter such as a recursive filter.

The model may include a limit for the maximum difference in green time or red time compared with a previous cycle that is independent of the demand values used in the model. For example, the model may only permit a cycle time to be incremented with larger demand by up to 5 sec or less.

The processing means may be part of the controller, or the radar detector apparatus, or both. It may be built into one of the traffic lights to form a "master" traffic light which generates the timing signals for one or more other lights of the junction.

The or each traffic signal may include a timing signal generating means that receives the weighted demand signal for that traffic signal from the processing means, and uses that demand signal to at least partially control the timing of the lights of the signal.

The timing signal means may generate drive signals for the lights of the traffic signal.

The timing signal generating means may set the green time and the red time for each signal in the system based on the weighted demand, and may also set the "all red" time for the junction which is the time at which all signals are red according to the weighted demand signal.

The timing signal generating means may receive additional signals from the controller that are based on the output signals of the radar apparatus. This may include a signal indicative of whether a radar signal can see the end of a line of traffic moving away from a traffic light associated with that radar apparatus, typically when the associated light is on red.

The timing signal generating means may also receive signals indicative of when a cyclist is approaching a signal, as indicated by the magnitude of a radar reflection being appropriate for a cyclist. When this is detected, the processing means may increase the all red time to all sufficient time for the cyclist to cross the junction. This time will be dependent on the spacing between the lights, i.e. how far the cyclist has to travel to cross the junction. The processing means may be arranged to combine the received signals with distance information stored in memory relating to the spacing between the lights.

The timing signal generating means may generate from the received signals from the radar apparatus a count of vehicles approaching the junction and a count of vehicle moving away from the junction, and may be adapted to compare the counts. In the event that the counts diverge by an amount above a predefined safe limit the processing means may raise an alarm since this may indicate that the radar information is unreliable. It may, when the counts diverge by an amount above a safe limit, stop using the demand signals as a basis for determining the timing for the traffic lights.

The two traffic lights (or more than two) may communicate by sending signals between one another wirelessly. The signals sent from one traffic light to another may include the weighted value.

Thus, one or both traffic lights may include a wireless transmitter for transmitting information from the radar detector apparatus or the controller to the other.

One of the traffic lights may function as a master signal, processing the weighted demand associated with each signal together to produce timing signals for the traffic lights. Each light may then act on response to the timing signals from the master signal.

These may be sent over hard wired connections or wirelessly to all the traffic lights.

In a refinement, the radar apparatus may be adapted to measure the speed of the approaching targets with the zone of detection. As the system knows the speed and the range of the approaching targets it can implement a safety cut-off function so that the light does not change from red to green if the approaching vehicle would not be able to stop in time.

The safety cut off would be implementing an inhibit to the call of a red signal when the signal was on green and the speed and range of the target was such that it violated set system boundary conditions on braking distances. E.g. a car at 30m away travelling at 50mph when the signal was on green could not be then shown a red signal. Alternatively, a vehicle passing a red signal may extend the signal inter-red time such that the other signal is inhibited going to green for a period related to the conditions.

The safety cut off may be based on pre-stored speed and distance information held in a

table.

In a further modification, the controller or each controller may be adapted to determine if a vehicle in the detection zone will pass the traffic signal on red, and to log information about the event such as the identity of the vehicle, the time, the speed of the vehicle and so on.

The system may include a camera that is located so that an image of a vehicle that has passed the traffic signal on red, or is approaching at a speed that will mean it has to pass on red, is captured.

The system may be arranged to log these events to; * Statistically analyse the event of signal violation occurring * And/or Deploy or trigger the camera to record the event The system may be adapted so that over time it will learn the relative position of a stop line associated with the traffic light by determining the section of the detection zone in which a vehicle stops that is nearest to the traffic signal when the light is red.

The system may learn by determining which section the nearest stopped vehicle is in for a number of cycles of red-green traffic light operation. For instance it may learn over at least 5 cycles following start-up of the system for the first time. Once learnt, the position may be stored in memory, or the system may learn continuously as it is used.

The applicant has appreciated that approaching targets at each traffic light signal may vary as the position that the vehicle is indicated to stop at the red light is usually different for each end. i.e. the range to the first target is usually different for each end so an offset could be created to further optimise the system. E.g. 10 cars one end may occupy a block from 15m to 55m from the signal but the same set of vehicles may occupy 5m to 45m at the other end. in this case, the values I5m and 5m will be learnt.

The invention can be applied to portable traffic light systems comprising more than two lights/approaches. 1.e. a multi-phase system. Thus, each phase may be provided with a traffic signal/radar/controller of the first aspect of the invention. The weighted values from each traffic light may be processed together.

The portable traffic light may be battery powered from a battery built into the traffic signal, or from an external battery source.

The radar detector and portable traffic light may be combined as a single portable apparatus, for instance with a traffic signal head and radar detector mounted to a common support. They may share a battery supply.

The radar detector and portable traffic light may be separate and may be connected by a wireless link or a wired connection. This would allow the traffic signal head and radar detector to be mounted in different locations, depending on the configuration of the zone that is being controlled to allow optimal siting of the signal head and the radar detector.

To allow the system to operate away from a mains power source, the radar apparatus of the invention may comprise a low power radar apparatus. By this we mean that it consumes less than 1 Watt of power, and preferably less than 500mWatts of power or perhaps less than 200mWatts. Conventional radar detectors used in the prior art consume more power and so are not as suitable for use in a portable traffic light.

To achieve a low power consumption the radar detector may be a low power radar detector. For example, the detector may be configured so that the duty cycle (the time spent transmitting versus time spent not transmitting) is set to be less than about 20 percent or perhaps less than 10 percent. This uses less power than a conventional radar with a higher duty cycle. A suitable radar detector that could be used is that sold under the product model 331 by the applicant which has been previously used in road side signs.

According to a second aspect the invention provides a portable control system suitable for controlling the flow of traffic across a controlled region of highway, such as a junction, that is controlled by one or more portable traffic lights, the control system comprising: a portable radar detector apparatus that in a position of use monitors a detection zone that extends over a region in front of the traffic light through which traffic approaching the traffic light passes, the radar detector generating an output signal that encodes information about any target vehicles identified in the zone of detection, and a controller that in use receives the output signal from the radar detector apparatus, the controller being arranged to derive from the signal output from the radar detector apparatus a demand signal and in which the controller is further adapted to determine the relative duration of the green to red signal for the light as a function of the demand signal.

The controller and the portable radar apparatus may be provided as a single unit,and may for instance include a common housing.

The system may be battery powered, and may include one or more batteries.

The controller may generate signals suitable for transmission to at least one portable traffic light that in a position of use controls the flow of traffic moving towards the traffic light that approaches the controlled region, the traffic light comprising a signal head including a set of lights that in use is located so that the lights are visible to vehicles approaching the traffic light; The system may include more than one radar apparatus and the controller may process the demand signals associated with each radar apparatus together to produce a weighted demand signal for each traffic signal.

There will now be described by way of example only, one embodiment of the present invention with reference to the accompanying drawings of which: Figure 1 is perspective view of an embodiment of a traffic light system according to the present invention installed at a road works on a highway; Figure 2 is a view of one of the traffic light signals used in the system of Figure 1; Figure 3 is a block diagram of the component parts of the radar detector apparatus associated with each traffic light signal; Figure 4 is a perspective view of the zone of detection of one of the radar detector apparatus; Figure 5 is a view from the side of the sections relative to a queue of vehicles when the light is red; and Figure 6 is a block diagram of the complete system showing the signals that pass between different parts of the system As shown in Figure 1, an embodiment of a two-signal traffic light system according to the present invention is located at a stretch of highway that is undergoing road works. in this example, the road works block one lane of the two way highway so that at any given time traffic can only flow along one line. if left uncontrolled there would be a risk of a head on collision between traffic flowing in each direction, or at best a risk of gridlock. The embodiment would equally/ work for controlling a junction rather than a stretch of road.

To make the highway safe during the road works a battery powered portable traffic light signal 10a, 10b is located at each end of the highway section. The lights of the traffic light signals arc timed so that only one traffic light shows a green signal at any given time, the other showing a red signal during those given times. By alternating between periods of red and green for each traffic light, vehicles can safely move along the single lane of highway. This is a typical use of portable traffic lights and is well known to the person skilled in the art.

Each traffic light signal is substantially of the same design as the other and one of the traffic lights 10 is shown in Figure 2 of the drawings. The traffic light signal is a portable unit, to be easily moved to site and later removed, allowing a portable system to be quickly and easily installed. The traffic light signal comprises a mast 12 that supports a signal head 14. The signal head includes three lights, a red light 16, amber light 18 and green light 20 as is conventional (there could be only two lights depending on the law of the arca in which the traffic light is to be located). The mast extends from a base 19 that is supported on a set of wheels 17. A drive circuit for the lights and battery (both not shown in Figure 2) are located within the base. An optional receiver for receiving wirelessly transmitted timing signals is included that outputs signals for the drive circuit. In some cases where arc hard wired connection to a source of timing signals is provided the receiver could comprise an input terminal.

To provide enhanced control of the traffic signals, the traffic light system of this embodiment is enhanced by providing two radar detector apparatus 30. In this example, each radar apparatus is supported by an extension pole 12a that extends away from the support mast for the traffic signal head.

Figure 3 shows a suitable radar apparatus in block diagram form. The radar apparatus comprises a microwave transceiver, and amplifier and signal conditioning circuit that receives signals from the transceiver caused by reflection of microwave energy from target vehicles, an analogue to digital converter that converts the amplified signals to the digital domain, and a digital signal processor. By appropriate selection of transmission signals and interpretation of the received signals, this apparatus can identify the presence of multiple targets in the field of view of the radar apparatus and can generate output signals that encode this information.

The radar apparatus in this example is a frequency modulated continuous wave radar (FMCW) type apparatus, although other types could be used. FMCW radars are known to be extremely well suited to the measurement of distance to targets. As such the radar detector of this embodiment is able to provide range detection capabilities, which has herebefore not been implemented in a portable traffic signal system.

A wide range of radar detectors could be used, but notably the apparatus should be chosen where possible to be of the type that consumes a low amount of power as otherwise it would place an excessive drain on the batteries used to power the portable apparatus. in this example the radar detector chosen has a power of less than 180mwatts, based on model number 331 sold by the applicant, details of which are available in the applicants product literature. The low power is achieved through a number of refinements including the use of a low duty ratio of 10 percent.

The output from the radar apparatus in this example therefore comprises a signal which encodes the location and speed of any targets located in the zone of detection of the radar beam. This signal is fed to a controller as explained later.

The beam of the radar apparatus is shown in Figure 4, looking down from above the highway. The beam can be seen to be directed onto a zone of detection in front of the traffic signal. Figure 3 shows the zone of detection for one signal 10a, the dotted line encompassing the edge of the zone of detection. As can be seen this zone overlays a portion of the highway in front of the traffic light signal.

The zone of detection 40 is the region within which vehicles are detected by processing the reflected radar signals "seen" by the radar detector. As shown the zone is broken down into sections 41, the boundary between each section shown by a dashed line extending across the highway. These sections are approx. 3m in length, and there may be n sections where n is between 10 and 50. Of course there could be as few as two sections and more than 50. in this embodiment the zone is therefore large enough to encompass multiple vehicles, or targets.

Each section is chosen to accommodate a single average size vehicle when there is a queue of vehicles in front of the traffic signal. Depending on the precise layout of the traffic controlled section and orientation of the radar detector, the first vehicle in a queue that forms when the light is red could be in any one of the first few sections.

Figure 5 shows that the front of the queue in this example is aligned with the second section, as indicated by the lead vehicle being positioned in the second section 41.

Of course, in a refinement the range detection ability may be used to look only at a small region of the highway through which traffic flows, smaller than one vehicle.

This is sufficient to enable a count of vehicles approaching the detector to be made, something only possible with the range detection functionality.

The output of the radar detectors is fed to a controller that is connected to the radar detector apparatus and respective traffic light. In a practical implementation as shown in Figure I, this controller may be located within the base of each traffic light signal. in an alternative, not shown, each controller may be integrated with the radar detector apparatus, or may be provided as a separate unit. In a modification not shown a single controller for both traffic lights may be provided.

The arrangement of traffic light signals, radar detector apparatus and controllers is shown schematically in figure 6 of the drawings. As can be seen, each controller receives information from the radar detector apparatus identifying the number of vehicles (targets), the location of each vehicle relative to the sections, and the speed of each vehicle. This information is refreshed every few seconds. The controller takes this information and from it produces a demand signal indicative of how much demand there is for the signal to be green. In essence if there are no targets there will be zero demand, and if each section contains a stationary vehicle (starting with the one at the front corresponding to the stop fine) then the demand will be deemed maximum.

The demand produced by each controller is then fed to a processing means. As shown this is a separate unit, but it may be combined with the controller of one of the traffic lights, or where a combined controller is provided may be integrated into the combined controller.

The processing means comprises an input for receiving the demand signals and a processor which generates a weighted demand signal for each traffic light based upon the values of the demand signals. It does this in real time, based on the instantaneous values of the demand signal.

The processing means supplies the weighted demand signals to a transmitter to send them wirelessly to a master traffic light signal. This signal include a timing generating means, in the form of a further signal processor. This generates actual timing signals for each light at the junction taking into account the value of the weighted demand signals. These timing signals are sent wirelessly to each traffic light where they are detected by a receiver and fed to a driver. The driver converts the timing signals into drive voltages to be applied to each light of the traffic lights.

The processing means in this example processes together the two demand signals to produce a weighted demand for each traffic signal that determines the ideal green time to be deployed for each signal to account for the identified traffic flow. Where possible the timing signal generating means will apply these ideal timings.

The system may be configured to produce a green time for each light that maximises the overall flow of traffic through the controlled portion of highway.

Alternatively, the processing means may give a higher priority to traffic approaching one traffic signal compared to the other, so for the same traffic demand at each traffic signal one may have a higher relative green time than the other.

The system may operate in a variety of ways, but in one practical implementation the system may operate as follows.

When in use the system may be arranged to recognise the relative weight of traffic demand at each signal and convert that to an optimised timing. This is achieved by processing the output signals from the radar apparatus. In the limiting case where no traffic is producing a demand at one signal and there is high vehicular demand at the other signal the system may provide such green time to the high demand to diminish the demand to zero. In this limiting case it may be prudent within the system to have green time maximum and green time minimum settings that the traffic demand cannot over-ride. If the high demand is not diminished within this pre-set maximum green time then a red signal may be called at the high demand signal and the system may progress such that a green minimum time may be applied at the signal with no demand before returning to continue diminishing the high demand.

In the condition where a green time is being serviced for one signal and is scheduled to finish owing to either the maximum green time expiring if a maximum is set or demand from the other signal has determined that the other green signal is scheduled to be called owing to the relative weight of demand of the traffic then the green may be extended. The green may be extended by a fixed time, say 2 seconds, if the radar determines that there is a vehicle at such distance and speed that will not be able to stop should a red light be applied at that instance in the timing. The green time that is applied may be variable depending on the position and speed of the vehicle as dctcrmincd by the radar.

The skilled person will understand that many modifications of the embodiment of Figure 1 are possible. There may be more than two traffic lights, and therefore more than two radar detectors apparatus. A weighted demand for each traffic light can then be produced based on the output of all the radar detectors. Alternatively, some traffic light signals in the system may be associated with a radar detector apparatus and others not associated with a radar detector apparatus. The timing for the lights without radar detector apparatus can be determined based on the demand at the traffic light signals that do have radar detector apparatus monitoring approaching traffic.

The current systems do not take into account the amount of traffic at each approach to a portable signal. Using smart radar measurements which estimate the amount of queuing or approaching traffic at each end will enable the controller timings to be dynamically altered so more green light time is deployed proportionally for the signal approaches with the highest vehicle demand.

Under current systems, if the lights were configured for equal maximum green time at each end but the traffic flow was such that twice as many cars approached from one end as compared to the other then a queue would start to form at the end with the higher demand. It is a quite usual experience for drivers who come across portable traffic lights where there are traffic conditions that are other than light' to see an imbalance of the system response to the traffic conditions.

The proposed new system seeks to dynamically optimise the timings such that a balanced system response is formed to the changing traffic conditions.

Claims

CLAIMS1 A portable traffic light system suitable for controlling the flow of traffic across a controlled region of highway, such as a junction, the portable traffic light system comprising: at least one portable traffic light that in a position of use controls a flow of traffic that is approaching the controlled region, the traffic light comprising a signal head including a set of lights that in use is located so that the lights are visible to vehicles approaching the controller region; a portable FMCW radar detector apparatus having a range detection capability which in a position of use monitors a detection zone that extends over a region in front of the traffic light at a defined range through which the flow of traffic approaching the traffic light must pass, the radar detector generating an output signal that encodes information about any target vehicles identified in the zone of detection, the information including the speed of a vehicle in the detection zone together with the associated position of the vehicle within the detection zone. anda controller that in use receives the output signal from the radar detector apparatus, the controller being arranged to derive from the signal output from the radar detector apparatus a demand signal and in which the controller is further adapted to determine the relative duration of the green to red signal for the light as a function of the demand signal.
2. A system according to claim I in which the radar detector apparatus is physically connected to the traffic light.
3. A system according to claim 1 or claim 2 in which, in the event that there are multiple targets in the zone of detection, the signal output from the radar detector apparatus encodes the location and speed of each target located in the zone of detection of the radar beam.
4. A system according to any preceding claim in which the radar detector apparatus has a low power consumption and operates with a duty cycle, defined as the ratio of the time spent transmitting versus time spent not transmitting that is is set to be less than 20 percent, or less than 10 percent.
5. A control system of any preceding claim which is battery powered and includes one or more batteries.
6. A system according to any preceding claim in which the radar detector apparatus outputs an output signal that additionally encodes one or more of the following items of information about vehicles in the zone: The number of vehicles approaching or stationary, either the detection zone or having crossed the zone; -Is a vehicle stationary (yes/no binary signal) The number of vehicles in each section of the zone where the zone is in sections and optionally their range or position.- The type of vehicle as indicated by the strength of reflected signal from one or more targets seen by the radar apparatus.
7. A system according to any preceding claim in which the controller divides the portion of highway in the detection zone ahead of the traffic signal into a plurality of segments and the radar detector apparatus and controller are adapted to measure the number of cars approaching the traffic signal that are within the detection zone and the number of segments of the detection zone that contain a stationary vehicle, an estimate of volume of traffic being generated by processing this information and the system being configured to use this estimate in producing the demand signal.
8. A system according to claim 9 in which the controller is adapted to estimate the demand as a function of the volume of traffic by adding the number of segments that are occupied by stationary vehicles to the number of vehicles approaching the rear of the queue of waiting vehicles to create a demand value.
9. A system according to any preceding claim in which the controller is adapted to produce timing signals that are supplied to the traffic lights whereby the higher the demand signal the higher the relative duration of green to red phase, and the lower the demand signal the lower the relative duration of the green to red phase.
10. A system according to any preceding claim comprising two or more portable traffic light signals each comprising: a traffic light signal head including a set of lights that in use is located so that the lights are visible to vehicles approaching the respective traffic light; and may include for at least two of the traffic lights a respective radar detector apparatus that monitors a detection zone which extends over a length of the highway approaching the respective traffic light through which traffic must pass or will be stationary approaching the traffic light, the detection zone of each radar detector apparatus being sufficiently large to contain a plurality of approaching vehicles.
11. A system according to claim 10 in which a respective controller is associated with each of the radar detector apparatus of each traffic signal.
12. A system according to claim 10 or claim 11 which further includes a processing means arranged to process together the two demand signals to produce a weighted demand for each traffic signal that takes account of the demand at each traffic signal.
13. A system according to claim 12 in which the weighted demand for each traffic signal determines a forced green time to be sent to each traffic light which determines when the light should turn green.
14. A system according to claim 13 which includes a processing means that in use generates weighted demand signals using an evolving model of flow of vehicles across the junction that is updated by the information contained in the output signals from radar apparatus or from the demand signals for each traffic signal/radar apparatus.
15. A system according to claim 14 in which the model generates weighted demand signals as a function of historical variations in the demand signal value over time.
16. A portable control system suitable for controlling the flow of traffic across a controlled region of highway, such as a junction, that is controlled by one or more portable traffic lights, the control system comprising: a portable FMCW radar detector apparatus that in a position of use monitors a detection zone that extends over a region in front of the traffic light through which traffic approaching the traffic light passes, the radar detector generating an output signal that encodes information about any target vehicles identified in the zone of detection, the information including the speed of a vehicle in the detection zone together with the associated position of the vehicle within the detection zone. anda controller that in use receives the output signal from the radar detector apparatus, the controller being arranged to derive from the signal output from the radar detector apparatus a demand signal and in which the controller is further adapted to determine the relative duration of the green to red signal for the light as a function of the demand signal.14. The control system of claim 13 in which the controller and the portable radar apparatus are provided as a single unit.15. The control system of claim 13 or 14 which is battery powered and includes one or more batteries.16. A system according to claim 13,14 or 15 in which the radar detector apparatus in use outputs an output signal that indicates the speed of a vehicle in the detection zone together with the associated position of the vehicle within the detection zone.
17. A system according to claim 16 in which, in the event that there are multiple targets in the zone of detection, the signal output from the radar detector apparatus encodes the location and speed of each target located in the zone of detection of the radar beam.
18. A system according to claim 16 or claim 17 in which the speed measurement is achieved by the range detection facility of the radar by measuring the change in position of identified target vehicles over time.
19. A system according to any preceding claim in which the radar detector apparatus has a low power consumption and operates with a duty cycle, defined as the ratio of the time spent transmitting versus time spent not transmitting that is is set to be less than 20 percent, or less than 10 percent.